Method for fabricating a through hole on a semiconductor substrate

ABSTRACT

A method for fabricating a through hole is disclosed. First, a conductive structure having a conductive layer and a cap layer are formed on a substrate. A patterned first photoresist layer is formed on the substrate and the conductive structure to define a pattern of the through hole. Then, a first etching process to remove the cap layer not covered by the first photoresist layer is performed until the conductive layer is exposed. The first photoresist layer is removed. A dielectric layer and a patterned second photoresist layer are formed on the substrate. Finally, a second etching process is performed to remove the dielectric layer not covered by the second photoresist layer until the conductive layer is exposed. The pattern of the second photoresist layer is the same as the pattern of the first photoresist layer.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to a method for fabricating a through hole, andmore particularly, to a method for fabricating a through hole byperforming two etching processes.

2. Description of the Prior Art

In semiconductor fabrication, in order to electrically connect device asmetal oxide semiconductor (MOS) transistors with each metal conductivelayer to form a complete electrical circuit, contact plugs and via plugsneed to be formed in dielectric layers for serving as conductive linesof the MOS transistors and metal conductive layers when performing amultilevel metallization process.

The conventional process for forming contact plugs and via plugsincludes performing an etching process to form through holes, such ascontact holes and via holes, in the dielectric layers, and filling withmetal materials with low resistivity into the contact holes and viaholes to form the contact plugs and the via plugs. Since through holemanufacture affects the reliability of the electrical connection betweentwo metal layers or conductive layers, it often becomes an importantfactor of the fabrication performance of the very large scaleintegration circuit.

Please refer to FIGS. 1–3. FIGS. 1–3 are schematic diagrams of a methodfor fabricating a through hole on a substrate 10 according to the priorart. As shown in FIG. 1, the substrate 10 comprises a conductivestructure 12, wherein the conductive structure serves as a gate, a wordline, a bit line, or a metal conductive line and comprises a metalconductive layer 14 and an anti-reflection coating (ARC) layer.According to the prior art, a dielectric layer 18 is formed on thesurface of the substrate 10 at first. Then, as shown in FIG. 2, apatterned photoresist layer 20 is formed on the surface of thedielectric layer 18 to define at least a through hole above theconductive structure 12. Then, as shown in FIG. 3, an etching process isperformed by taking the photoresist layer 20 as an etching mask toremove the dielectric layer 18 and the ARC layer 16 not covered by thephotoresist layer 20 until the surface of the conductive layer 14 isexposed. Finally, the photoresist layer 20 is removed to accomplish thefabrication of the through hole 22.

Referring to FIG. 3, during the etching process using the photoresistlayer 20 as the etching mask, the ARC layer 16 is etched in situ afterthe dielectric layer 18, which means the ARC layer 16 and the dielectriclayer 18 are etched in the same reaction chamber. Generally, when theconductive layer 14 is composed of metal materials, such as alloy of Aland Cu, the ARC layer 16 will be composed of TiN, Ti, or the combinationthereof, and the dielectric layer 18 will be composed of oxide.Therefore, CF₄, CHF₃, or other etching gases with high selectivity tooxide materials are chosen as the etching agent since the dielectriclayer 18 is the primary etching object. However, the above-mentionedetching gases have low etching rates in the ARC layer 16 composed ofTiN/Ti. Accordingly, the photoresist layer 20 serving as an etching maskis required to have a quite thick thickness to sustain a quite long timeof the etching process until the ARC layer 16 is completely opened.During a longer etching process, corners being cut or collapse problemmay possibly occur on the thicker photoresist layer 20. In addition,when the ARC layer 16 is being etched, the dielectric layer 18positioned on the ARC layer 16 may be affected by the etching gas sothat the through hole 22 will have an irregular sidewall. Furthermore,residues resulting from the removed ARC layer 16 may be formed on thesidewall of the dielectric layer 18 when etching the ARC layer 16, andsuch residues are hard to remove from the dielectric layer 18 so thatthe quality of the through hole 22 is degraded.

SUMMARY OF INVENTION

It is therefore a primary objective of the claimed invention to providea method for fabricating a through hole that can remove the ARC layerwith high efficiency to solve the above-mentioned problem.

According to the claimed invention, a method for fabricating at least athrough hole on a substrate is provided. The method includes forming aconductive structure having a conductive layer and a cap layer on thesubstrate, forming a patterned first photoresist layer on the substrateand the conductive structure to define at least a pattern of the throughhole, performing a first etching process to remove the cap layer notcovered by the first photoresist layer until the conductive layer isexposed, removing the first photoresist layer, forming a dielectriclayer and a patterned second photoresist layer on the substrate insequence, wherein the pattern of the second photoresist layer is thesame as the pattern of the first photoresist layer, and performing asecond etching process to remove the dielectric layer not covered by thesecond photoresist layer until the conductive layer is exposed.

It is an advantage of the claimed invention that the ARC layer isanteriorly etched before the dielectric layer is formed so that anetching agent having high etching selectivity to the ARC layer can beused to effectively remove the ARC layer. Accordingly, a thinnerphotoresist layer can be used as the etching mask in the second etchingprocess for etching the dielectric layer because the longer etchingprocess for etching the ARC layer in the prior art is not neededanymore. In this situation, the problem of corners being cut orcollapsing of the photoresist layer can be avoided. Furthermore, becausethe thickness of the photoresist layer of the claimed invention isthinner than that of the photoresist layer in prior art method, thedesign of circuit layout and line width can be advanced to increase theintegration of the semiconductor devices.

These and other objectives of the claimed invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment, which isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1–3 are schematic diagrams of a method for fabricating a throughhole on a substrate according to the prior art.

FIGS. 4–10 are schematic diagrams of a method for fabricating at least athrough hole on a substrate according to the present invention.

DETAILED DESCRIPTION

Please refer to FIGS. 4–10. FIGS. 4–10 are schematic diagrams of amethod for fabricating at least a through hole on a substrate 30according to the present invention. As shown in FIG. 4, a metalconductive layer 32 and an ARC layer 34 are formed on the surface of thesubstrate 30, wherein the substrate 30 may further have a plurality ofprefabricated semiconductor elements and dielectric layers. The metalconductive layer 32 is composed of usual conductive materials ofsemiconductor process, such as aluminum alloy or aluminum copper alloy.The ARC layer 34 is used to reduce the high reflectivity of the metalconductive layer 32 to insure the accuracy and performance of thephotolithography and etching process, and thereby the ARC layer 34 iscomposed of materials which can meet this requirement, such as TiN/Ti.

As shown in FIG. 5, a photolithography and etching process is performedto form a patterned photoresist layer (not shown) on the ARC layer 34 todefine a conductive line. Then, the patterned photoresist layer is takenas an etching mask to perform an etching process for removing a portionof the ARC layer 34 and a portion of the metal conductive layer 32 sothat a conductive structure, the conductive line 36, is formed. Afterthat, the fabrication of through holes is performed above the conductiveline 36. Referring to FIG. 6, a first photoresist layer 38 is formed onthe substrate 30, and a photolithography process is performed to defineat least a through hole pattern on the photoresist layer 38 locatedabove the conductive line 36. Then, as shown in FIG. 7, a first etchingprocess is performed by taking the first photoresist layer 38 as anetching mask to remove the ARC layer 34 not covered by the firstphotoresist layer 38 until a first portion of the metal conductive layer32 is exposed. After the first etching process, the first photoresistlayer 38 is removed.

Since the main object of the first etching process is the ARC layer 34,the etching agent is selected according to if the etching agent has abetter etching selectivity to the ARC layer 34 or not. For example, ifthe ARC layer 34 is composed of TiN/Ti, the etching agent is selectedfrom the group consisting of BCl₃/Cl₂, CCl₄, and SF₆ so that the exposedTiN/Ti ARC layer 34 can be removed more rapidly. In addition, as both ofthe former etching process for forming the conductive line 36 and thisfirst etching process are meant for removing a portion of the ARC layer34, these two etching processes can utilize the same etching agent andcan be performed in the same reaction chamber. In addition, because onlythe ARC layer 34 is the etching object of the first etching process, thethickness of the first photoresist layer 38 used as the etching mask canbe thinner provided that it can sustain the first etching process untilthe ARC layer 34 is opened.

Please refer to FIG. 8. A dielectric layer 40 is then formed on thesubstrate 30, and meanwhile, the opening of the ARC layer 34 is filledwith the dielectric material. A chemical mechanical polishing process ora thermal flow process is optionally performed to planarize the surfaceof the dielectric layer 40. Referring to FIG. 9, a patterned secondphotoresist layer 42 is formed on the dielectric layer 40, wherein thepattern of the second photoresist layer 42 is the same as the pattern ofthe first photoresist layer 38 to define the through hole on theconductive line 36. Then, a second etching process is performed bytaking the second photoresist layer 42 as an etching mask to remove thedielectric layer 40 not covered by the second photoresist layer 42 untilthe first portion of the metal conductive layer 32 is exposed. If thedielectric layer 40 is composed of oxide, an etching gas having highetching rate to the oxide layer, such as CHF₃, CF₄, or Ar, can beselected as the etching agent of the second etching process. Finally,the residual second photoresist layer 42 is removed to accomplish thefabrication of the through hole 44, as shown in FIG. 10.

The following process of filling conductive materials into the throughhole 44 for fabricating a contact plug includes forming a glue layer,such as a Ti/TiN layer, on the surface of the sidewall of the throughhole 44, and filling the through hole 44 with conductive materials, suchas tungsten, so that the conductive line 36 can be electricallyconnected to the posteriorly formed conductive elements positioned onthe dielectric layer 40. The fabrication process of contact plugs is awell-know process to those skilled in the art, thus no extraneousdescription will be provided herein. In addition, in another embodimentof the present invention, a metal material, e.g. aluminum, can be usedto directly fill the through hole 44. Then an etching process isperformed to the metal material positioned on the dielectric layer 40 toform metal conductive lines above the dielectric layer 40 and toelectrically connect the upper metal conductive line and the conductiveline 36 simultaneously.

The present invention method can be applied to any fabrication processfor electrically connecting the conductive layers positioned below andabove the dielectric layers or any fabrication process of through holes,such as contact holes, via holes, and through holes above gatestructures or dual damascene structures. This means the presentinvention method can be utilized in any applications for fabricating athrough hole on a conductive layer having a cap layer thereon, whereinthe cap layer has a different etching selectivity from that of thedielectric layer positioned on the cap layer so as to fabricate thethrough holes with better profiles and save the process time. Forexample, when the conductive layer and the cap layer are a dopedpolysilicon layer and a nitride layer respectively, it is appropriate toapply the present invention method. It should be noticed that thebarrier layers, ARC layers, mask layer, or passivation layers ofsemiconductor process are all included in the definition of the caplayer according to the present invention. On the other hand, a machinewith lower fabrication functionality can be utilized to perform aprocess used to be performed with machines with higher fabricationfunctionality according to the spirit of the present invention.Consequently, existing equipment and machines can still be used when thedesign standards of products are changed to more accuracy, withoutaffecting the machines. For example, when the thickness of elementmaterial becomes thicker according to the design requirement, accordingto the present invention, a machine with lower etching functionality canstill be used to etch the specific material in several stages by usingthe machine with higher etching functionality, so that the cost ofequipment can be saved.

In contrast to the prior art, the present invention method performs theetching process for forming a through hole in two stages: a firstetching process to etch the cap layer for forming a through hole patternin the cap layer, and a second etching process to etch the dielectriclayer formed on the cap layer for forming the through hole pass throughthe dielectric layer and the cap layer. Since each of the first andsecond etching processes can use an etching agent with high etchingselectivity for its own etching object, the cap layer and the dielectriclayer respectively, completely opening the cap layer is guaranteedaccording to the present invention. Even when the cap layer is thickerthan a conventional thickness of the cap layer, the thicker cap layercan still be opened with the first etching process effectively.According to the present invention, the sidewall of the through hole canhave a better profile, and the etching rate can be increased so that thetime of etching the cap layer can be reduced. Therefore the efficiencyof fabrication process can be raised. Furthermore, the secondphotoresist layer taken as the etching mask is thinner than that of theprior art, thus the problem of collapse of the photoresist layer can beavoided. Accordingly, for the photolithography process, an advanceddesign with smaller line width and higher density can be applied.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A method for fabricating a through hole comprising: forming aconductive structure on a substrate, wherein the conductive structurecomprises at least a conductive layer and a cap layer positioned on theconductive layer; forming a patterned first photoresist layer on thesubstrate and the conductive structure to define at least a pattern of athrough hole; performing a first etching process to remove the cap layernot covered by the first photoresist layer until at least a firstportion of the conductive layer is exposed; removing the firstphotoresist layer; forming a dielectric layer and a patterned secondphotoresist layer on the substrate in sequence, wherein a pattern of thesecond photoresist layer is the same as a pattern of the firstphotoresist layer; and performing a second etching process to remove thedielectric layer not covered by the second photoresist layer until thefirst portion of the conductive layer is exposed.
 2. The method of claim1, wherein the conductive layer is a metal layer, and the cap layer isan anti-reflection coating (ARC) layer.
 3. The method of claim 1,wherein the step of forming the conductive structure on the surface ofthe substrate comprises: forming the conductive layer on the substrate;forming the cap layer on the conductive layer; forming a patterned thirdphotoresist layer on the cap layer to define the conductive structure;performing a third etching process by taking the third photoresist layeras an etching mask to remove the cap layer and the conductive layer notcovered by the third photoresist layer; and removing the thirdphotoresist layer.
 4. The method of claim 3, wherein the first etchingprocess and the third etching process are performed in the same reactionchamber.
 5. The method of claim 3, wherein the first etching process andthe third etching process utilize the same etching agent.
 6. The methodof claim 2, wherein the metal layer comprises an aluminum alloy layer.7. The method of claim 2, wherein the ARC layer comprises a titaniumnitride or/and titanium (TiN/Ti) layer.
 8. The method of claim 7,wherein the etching agent of the first etching process is selected fromthe group consisting of BCl₃/Cl₂, CCl₄, and SF₆.
 9. The method of claim1, wherein the conductive layer comprises a doped polysilicon layer, andthe cap layer comprises a silicon nitride layer.
 10. The method of claim1, wherein the dielectric layer comprises an oxide layer.
 11. The methodof claim 10, wherein an etching agent of the second etching process isselected from the group consisting of CHF₃, CF₄, and Ar.